The invention relates to a furnace for the heat treatment of mostly lumpy to fine grained material, particularly shaft furnaces, rotary furnaces or the like. The furnace functions for the calcining or sintering of limestone, dolomite or magnesite, and wherein the calcining material passes through a preheating zone, a calcining zone, and a cooling zone. The calcination zone has a gas feed or gas discharge device, respectively, and a calcination device as well as a gas-conveying device for the production of a hot gas circulation.
From German Pat. No. 1,034,090, a transverse flow shaft furnace is known which has gas collecting devices and heating devices. The hot gases required for the sintering of the calcining material are collected after flow-through of the material layer in the gas collecting devices and are reheated in the heating devices by means of injectors for the gas circulation. The conveyor means required for the gas circulation are in this connection provided as rigid injectors which circulate an essentially constant volume of fed-through hot gases. Disturbances occur with such a transverse or cross flow shaft furnace especially when, on account of an altered bulk density in the shaft and therefore altered pressure drag in the material column, the gas volume available to the particular injector is altered.
From the German Pat. No. 1,558,057, a shaft furnace heated by transverse flow for the calcination of limestone is known, which has in the passage direction of the material a preheating zone, two calcination zones, and a cooling zone, whereby each calcination zone has quasi-closed hot gas circulation. The hot gas circulation is carried out such that each calcination zone is correlated with at least one jet blower or injector, respectively, which produces the kinetic energy necessary for the hot gas circulation. The circulation of the hot gases takes place from the injector into a calcination chamber, a gas collection chamber, the correlated calcination material layer, the discharging gas collection chamber, and through a circulation channel back to the injector. In the calcination chamber, fuel, and, as combustion air, cooling air from the cooling zone is introduced. Through the intensive hot gas circulation there results a very uniform calcination over the entire shaft cross-section. It has been shown, however, that with the trend towards always larger furnace units, that the initiation of jet blowers or injectors causes limits to be established for the maintenance of the gas circulation in each calcination zone. These limits have to do particularly with the high construction cost for these injectors. In the second place, with these injectors, for each calcination zone with large furnace units, only insufficient drops in pressure of up to about 70 mm water column can be produced, so that with the large furnace units, the kinetic energy required for the hot gas circulation can no longer be produced with injectors. Therefore, only furnace units up to 120 tons output per day are known.